NCP1200 ON Semiconductor, NCP1200 Datasheet - Page 11

• Manufacturer Part Number: NCP1200
• Description: Current Mode Controller Fixed Frequency Operation
• Manufacturer: ON Semiconductor

internal parasitic SCR activation. One of them consists in
inserting a resistor in series with the high-voltage pin to
keep the negative current to the lowest when the bulk
becomes negative (Figure 22). Please note that the negative
spike is clamped to –2 x Vf due to the diode bridge. Please
refer to AND8069/D for power dissipation calculations.
A Typical Application
adapter. This is a typical application where the wall-pack
must deliver a raw DC level to a given internally regulated
apparatus: toys, calculators, CD players etc. Due to the
Simple and inexpensive cures exist to prevent from
Figure 24 depicts a low-cost 3.5 W AC-DC 6.5 V wall
Figure 22. A simple resistor in series avoids any
Figure 21. A negative spike takes place on the Bulk capacitor at the switch-off sequence
+
Cbulk
latchup in the controller
1
2
3
4
8
7
6
5
2
1
3
+
Rbulk
> 4.7 k
CV
CC
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NCP1200
11
V
sooner and thus stops the switching activity before the bulk
capacitor gets deeply discharged. For security reasons, two
diodes can be connected in series.
inherent short-circuit protection of the NCP1200, you only
need a bunch of components around the IC, keeping the final
cost at an extremely low level. The transformer is available
from different suppliers as detailed on the following page.
CC
Another option (Figure 23) consists in wiring a diode from
Figure 23. or a diode forces V
to the bulk capacitor to force V
+
Cbulk
UVLOlow sooner
1
2
3
4
8
7
6
5
CC
CC
3
to reach
to reach UVLOlow
1
+
CV
D3
1N4007
CC